Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent Is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture. The invention suggests a method of separation of ethanol and ethyl acetate, and ethanol and water by distilling a mixture of the components by way of an extractive distillation process in the presence of an extractive distillation solvent.
The present invention relates to the separation of components from ethanol mixtures thereof by extractive distillation.
Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture.
The separation of ethanol and ethyl acetate is complicated due to the existence of an azeotrope. Trimethylbenzene has been proposed in the literature as extractive distillation solvents to produce ethanol as distillate.
The separation of ethanol and water is complicated due to the existence of an azeotrope. Azeotropic distillation using benzene or cyclohexane is commonly used to effect the separation. Membrane separation, such as pervaporation, may alternatively be used to break the azeotrope. Pressure swing distillation is another separation method that may be used to produce pure ethanol and pure water. All of these methods utilize two distillation columns. In the case of azeotropic distillation, a phase separation device is needed. In the case of membrane separation, membrane modules are needed. Extractive distillation can also be used to effect the desired separation. This method also uses a two column system but the operation is simple. Ethylene glycol has been proposed in the literature as an extractive distillation solvent for the system ethanol/water.
As has been stated in U.S. Pat. No. 5,800,681 (Berg) extractive distillation is the method of separating close boiling compounds from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive distillation solvent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is Introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component.
It is an object of this invention to suggest at least one further extractive distillation solvent for the separation of components from ethanol mixtures thereof.
According to the invention, a method of separation of ethanol from a mixture of ethanol and another compound selected from a first group consisting of ethyl acetate and water, includes the step of distilling the mixture containing at least ethanol and another compound selected from a first group consisting of ethyl acetate and water by way of an extractive distillation process in the presence of an extractive distillation solvent selected from a second group consisting of an amine, an alkylated thiopene, a paraffin and a chlorinated carbon.
The mixture may contain ethanol and ethyl acetate and the extractive distillation solvent may be selected from the group consisting of an amine, an alkylated thiopene and a paraffin.
The ethanol and ethyl acetate mixture may contain only ethanol and ethyl acetate.
The amine may be selected from a group consisting of N,Nxe2x80x2-dimethyl-1, 3-propanediamine, N-Nxe2x80x2-dimethylethylenediamine, diethylene triamine, hexamethylene diamine and 1,3-diaminopentane.
The alkylated thiopene may be ethyl thiopene.
The paraffin may be at least one of the components selected from the group consisting of dodecane, tridecane and tetradecane.
The mixture may contain ethanol and water and the extractive distillation solvent may be selected from the group consisting of an amine and a chlorinated hydrocarbon.
The ethanol and water mixture may contain only ethanol and water.
The amine may be selected from a group consisting of diaminobutane, 1,3-diaminopentane and diethylene triamine.
The chlorinated hydrocarbon may be hexachlorobutadiene.